Cook's Note: You can buy the squid cleaned, but make sure it has the tentacles on it.
Rinse the squid inside and out and set aside. Heat half of the olive oil in a frying pan over medium heat and saute the eggplant, bell pepper and zucchini. Season with salt and black pepper, remove from the heat and stir in the buffalo mozzarella, making sure it doesn't melt.
Gently stuff the vegetables and cheese into each calamari. (Don't overstuff because when they cook, the squid shrink and you don't want the stuffing to pop out.) Seal the opening by threading the tentacles through the body with a toothpick a few times.
Heat the remaining olive oil with the garlic in another frying pan. Add the stuffed calamari and cook about 1 minute, and then add in the capers, tomatoes and olives.
Remove the garlic and add a pinch of salt, if desired. Cook about 3 minutes longer, and then serve immediately.